1. Field of the Presently Disclosed and Claimed Inventive Concept(s)
The presently disclosed and claimed inventive concept(s) relates generally to a hydraulic composition with a prolonged open time. More particularly, the composition comprises at least one cement retarder and at least one accelerator. The presently disclosed and claimed inventive concept(s) further relates to a dry mortar composition comprising the hydraulic composition having prolonged open time without deterioration of the other cement tile adhesive properties such as workability, setting time, strength development and sag resistance.
2. Background and Applicable Aspects of the Presently Disclosed and Claimed Inventive Concept(s)
Tiles have long been used as a finishing material for construction of buildings with a beautiful external appearance, convenience for installation, hygienic properties, convenience for cleaning, maintaining, and managing buildings, and the like.
Traditional cementitious tile adhesives (CTA) used to be simple dry mixtures of cement and sand. The dry mixture is mixed with water to form a wet mortar. These traditional mortars, per se, have poor fluidity or trowellability. Consequently, the application of these mortars is labor intensive.
Moreover evaporation of water into the air and especially the absorption of water through porous substrates on which the CTA is applied lead to a depletion of water in the wet mortar over time. Consequently, not enough water remains in the mortar resulting in very short open time, correction time and even issues with adhesion to the substrate. Additionally, a lack of sufficient water for the proper hydration of cement results in insufficient and incomplete strength development of the CTA.
Nowadays, in general, cellulose ethers are added to the mortar to reduce water loss due to evaporation and absorption of the substrate. Cellulose ethers provide water retention, thus water loss is strongly diminished but not completely prevented. But constant workability, acceptable correction and open time and especially proper strength development is provided.
Open time of a mortar is the time in which a tile can still be placed in the applied mortar and sufficient wetting of the tile with tile adhesive is assured. The end of the open time is indicated by having insufficient wetting of CTA on the backside of the tile. Open time is limited due to drying as well as other chemical and physical reactions related to the set of cement and effects of other used additives like cellulose ethers and redispersible polymer powders.
A method of extending open time by adding organic and/or inorganic cement hydration retarders to a cement mortar has widely been used. Through the addition of retarders the hydration reactions are decelerated or delayed. Consequently the setting and hardening of the mortar is shifted and open time is prolonged.
Setting time is defined in ASTM C266-65. Basically setting time is the time a mortar takes to set or harden at a given thickness. For construction using a cement-based hydraulic composition such as mortar or concrete, the control of setting time is desired with a view to ensuring workability, shortening the construction time and simplifying a curing facility. As demand for a setting accelerating effect in particular is growing so as to shorten the construction time, a setting accelerator having a high setting accelerating effect has been developed.
The delay in cement hydration reactions and consequently in setting time in general comes along with decreased strength development. In general, the slower the cement hydration, i.e., the longer the setting time, the higher is the risk of water loss and thus of insufficient strength development.
If a cementitious tile adhesive has a long open time with addition of a cement retarder, the long open time is established. However, the setting time is undesirably prolonged. So, there is a need to have a cementitious tile adhesive having a long open time with a comparable setting time.
Surprisingly, it has been found that the positive gain in open time by usage of a cement retarder is not reversed if an accelerator is added to compensate the cement set retardation. It has even been found that a retarder-accelerator combination can generate a synergistic effect, meaning that the combination can even have a longer open time compared with a retarder alone.